Solvent effects on chemical exchange in a push-pull ethylene as studied by NMR and electronic structure calculations

NMR measurements of chemical exchange in a push-pull ethylene, dissolved in a number of different solvents, are presented. These are complemented by high-level electronic structure calculations, using both gas-phase conditions and those which simulate solvents. The results show that it is essential to include entropy effects in order to understand the observed trends. For instance, the equilibrium state in this case represents the state with lowest Gibbs free energy, as it must, but not the lowest enthalpy. The particular molecule is methyl 3-dimethylamino-2-cyanocrotonate (MDACC). The geometry at the carbon-carbon double bond can be either E or Z with roughly equal populations at ambient temperature. We have measured the equilibrium constant and the rates for the exchange between these states in a number of solvents: methanol, chloroform, acetonitrile, toluene, dichloromethane, acetone, and tetrahydrofuran. Furthermore, the N,N-dimethylamino group attached to the double bond also shows restricted rotation, and this has been measured in both the E and Z conformations. The equilibrium constant and the three rotational barriers provide excellent probes of the solvent effects. Electronic structure calculations with a number of basis sets up to the 6-311++G(2df,2p) level, using both Hartree-Fock and density functional (B3LYP) methods were used to predict the E and Z ground states, and the three transition states. The calculations were done for an isolated molecule and also for solvent models representing toluene, acetone, and ethanol. The E conformation is more stable in solution, is the structure in the crystal, and is also the prediction for the gas phase from the calculations. However, the dependence of the equilibrium constant on temperature shows that the Z conformation actually has lower enthalpy. The stability of the E conformation in solution must be due to entropic effects. Similarly, the solvent effect on the E-Z barrier is primarily due to entropy. The measured enthalpy of activation is similar in all the solvents, but the entropy of activation increases with the solvent polarity. The barrier to rotation of the N,N-dimethylamino group shows a combination of entropy and enthalpy effects. This combination of experiments and theory gives an extraordinarily detailed picture of solvent-solute interactions.     

Amperometric Sniffer Based on Electrodes Supported on Ion‐Exchangers for Monitoring the State of Turning Rancid of Lipids

A porous gold electrode supported on one face of an ion‐exchange membrane, acting as a solid polymer electrolyte (SPE), is proposed as an amperometric sniffer for monitoring the aldehyde content in the headspace in equilibrium with lipid samples, in order to gain indication of their state of turning rancid It was used as a detector for a flow injection system in which aldehydes were injected, after preconcentration by solid phase microextraction on a SPME fiber from the gas phase standing above thermostated samples and subsequent desorption by heating. Repeatable (±4.5%) sharp peaks were detected over a wide linear concentration range (0.5–200 ppm). A detection limit of about 0.03 ppm was inferred for a signal‐to‐noise ratio of 3, referred to hexylaldehyde (used as prototype) dissolved in squalene or vegetable oils samples. This approach was applied to the determination of volatile aldehydes from some partially oxidized cereal oils and the results found were compared with both the corresponding peroxide values and their aldehyde content determined by a conventional spectrophotometric method.     

Combined use of X-ray photoelectron and Mössbauer spectroscopic techniques in the analytical characterization of iron oxidation state in amphibole asbestos

Asbestos fibers are an important cause of serious health problems and respiratory diseases. The presence, structural coordination, and oxidation state of iron at the fiber surface are potentially important for the biological effects of asbestos because iron can catalyze the Haber–Weiss reaction, generating the reactive oxygen species ?OH. Literature results indicate that the surface concentration of Fe(III) may play an important role in fiber-related radical formation. Amphibole asbestos were analyzed by X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy, with the aim of determining the surface vs. bulk Fe(III)/Fe_tot ratios. A standard reference asbestos (Union Internationale Contre le Cancer crocidolite from South Africa) and three fibrous tremolite samples (from Italy and USA) were investigated. In addition to the Mössbauer spectroscopy study of bulk Fe(III)/Fe_tot ratios, much work was dedicated to the interpretation of the XPS Fe2p signal and to the quantification of surface Fe(III)/Fe_tot ratios. Results confirmed the importance of surface properties because this showed that fiber surfaces are always more oxidized than the bulk and that Fe(III) is present as oxide and oxyhydroxide species. Notably, the highest difference of surface/bulk Fe oxidation was found for San Mango tremolite—the sample that in preliminary cytotoxicity tests (MTT assay) had revealed a cell mortality delayed with respect to the other samples.     

Photopolymerization of a perfluoropolyether oligomer and photolithographic processes for the fabrication of microfluidic devices

A perfluoropolyether based photocured polymer is proposed as structural material for the fabrication and easy prototyping of microfluidic devices. The kinetics of photopolymerization and the fluoropolymer characterization is reported, assessing the suitability of the material: it results transparent, thermally resistant, with a good dimensional stability and a chemical resistance much higher than polydimethylsiloxane, material currently used in microfluidics. The direct fabrication of microchannels is finally presented by direct photopolymerization under UV light irradiation through photomasks: the transfer of micropatterns was successful.     

Occupational exposure to complex mixtures of volatile organic compounds in ambient air: desorption from activated charcoal using accelerated solvent extraction can replace carbon disulfide?

A desorption study of 57 volatile organic compounds (VOCs) has been conducted by use of accelerated solvent extraction (ASE) and gas chromatography–mass spectrometry. Different solvents were tested to extract activated charcoal tubes with the objective of replacing carbon disulfide, used in official methods, because of its highly toxic health and environmental effects. Extraction conditions, for example temperature and number of cycles, were investigated and optimized. The definitive extraction procedure selected was use of acetone at 150 °C and two consecutive extraction cycles at a pressure of 1,500 psi. Considering a sample volume of 0.005 Nm³, corresponding to a sampling time of 8 h at a flow rate of 0.01 L?min^?1, the method was validated over the concentration range 65–26,300 μg?Nm^?3. The lowest limit of quantification was 6 μg?Nm^?3, and recovery for the 93 % of analytes ranged from 65 to 102 %. For most of the compounds, relative standard deviations were less than 15 % for inter and intra-day precision. Uncertainty of measurement was also determined: the relative expanded uncertainty was always below 29.6 %, except for dichlorodifluoromethane. This work shows that use of friendlier solvent, for example acetone, coupled with use of ASE, can replace use of CS₂ for chemical removal of VOCs from activated charcoal. ASE has several advantages over traditional solvent-extraction methods, including shorter extraction time, minimum sample manipulation, high reproducibility, and less extraction discrimination. No loss of sensitivity occurs and there is also a salutary effect on bench workers’ health and on the smell of laboratory air.

Synthesis of Porphyrin‐Anthraquinone Conjugates as Photosensitizing Agents

A series of 5,10,15,20‐tetraarylporphyrins covalently linked to anthraquinones belonging to the class of emodin were synthesized following two different pathways. The first method exploits the functionalization of the methyl group in position 6 of O‐protected emodins, which can be converted either into a carboxylic acid or into a bromo‐methyl derivative. The modified emodins were then bound through amido or ether bonds to one of the tetraarylporphyrins meso phenyl rings bearing an amino or hydroxyl group, respectively. An alternative synthesis exploits the mixed condensation of triacetoxy‐emodinaldehyde (or trimethoxy‐emodinaldehyde) with pyrrole in the presence of variable amounts of benzaldehyde, thus affording two similar 5‐emodin‐10,15,20‐triphenylporphyrins differing from one another in the emodin hydroxyl group protection. These compounds are characterized by direct conjugation of the emodin moiety to the tetrapyrrolic ring. Preliminary experiments were performed in vitro on the human colon adenocarcinoma cell line HCT116 to evaluate the photocytotoxicity of the new compounds.     

Iridoid glucosides from Viburnum chinshanense

The phytochemical study of the aerial parts of Viburnum chinshanense Graebn., a species growing in Western and Central China, led to the isolation of six iridoid glucosides: the novel 10,2'-diacetylpatrinoside, 1, and the known 2'-acetyldihydropenstemide, 2'-trans- p-coumaroyl-dihydropenstemide, 2'-acetylpatrinoside, decapetaloside, and patrinoside. In addition, amentoflavone and rosarin were also isolated.     

Phenolic content and in vitro antifungal activity of unripe grape extracts from agro-industrial wastes

The antifungal activity of unripe grape extracts from agro-industrial wastes has been evaluated against several strains of Candida spp. and dermatophytes. All the extracts tested showed antifungal activity. The geometric mean MIC ranged from 53.58 to 214.31 μg/mL for Candida spp. and from 43.54 to 133.02 μg/mL for dermatophytes. The chemical analyses have been carried out using Liquid Chromatograph equipped with a DAD and MS detectors. Flavan-3-ols were the main metabolites within all samples ranged from 3.3 to 6.8 mg/g fresh weight. For Candida spp. highest negative significant correlation has been found between MICs and polymeric flavan-3-ols (r = ?0.842; p < 0.001) and for dermatophytes between MICs and caffeoyl derivatives (r = ?0.962; p < 0.01). The results indicate that total extracts obtained from unripe grapes, a large source of waste material derived from the wine industry, could be used as a cheap source of value-added products.     

A new iridoid diglucoside from Harpagophytum procumbens

A new iridoid diglucoside has been isolated from an aqueous extract of Harpagophytum procumbens secondary roots, together with six known compounds. Its structure has been assigned as 6′-O-glucopyranosyl-8-O-trans-coumaroylharpagide by spectroscopic means.     

Secondary metabolites from Scrophularia canina L.

A re-examination of Scrophularia canina L. confirmed the presence of iridoid glucosides considered as chemotaxonomic markers for the Scrophulariaceae family, like aucubin, harpagide and 8-O-acetylharpagide, besides the further presence of 8-epiloganic acid, which is, indeed, considered the biogenetic precursor of iridoids normally found in Scrophulariaceae, and was recognised here for the first time in the studied species. Also verbascoside and (E)-phytol were evidenced for the first time in S. canina. The former compound is an almost ubiquitous glycosidic phenyl-ethanoid, which attains systematic importance when in co-occurrence with iridoids, and its taxonomical implications were discussed. The latter compound, even though it is omnipresent, is interestingly endowed with several biological activities, which may give an additional reason for the traditional uses of this plant.